[FIXED] Java Servlets - HTTP Status 500 Error instantiating servlet class

Issue

I am trying to instantiate my servlet but I am getting this 500 Status Error. I have read other posts but none of the proposed solutions seem to apply to my error.

My SampServlet Class

package com.example;

import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.annotation.*;
import java.io.IOException;
import java.io.PrintWriter;

@WebServlet(name = "SampServlet", value = "/SampServlet")
public class SampServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //define that we want to send HTML to our browser
        response.setContentType("text/html");
        // create our PrintWriter that allows us to write out text as well as write HTML to the screen
        PrintWriter out = response.getWriter();
        try {
            out.println("<h3>Testing Servlets</h3>");
        }
        finally {
            out.close();
        }
    }
}

my web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0">
    <servlet>
        <servlet-name>SampServlet</servlet-name>
        <servlet-class>com.example.SampServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>SampServlet</servlet-name>
        <url-pattern>/SampServlet</url-pattern>
    </servlet-mapping>
</web-app>

Project Structure enter image description here

the error I'm getting when I go to http://localhost:8080/SampServlet

Message Error instantiating servlet class [com.example.SampServlet]

Description The server encountered an unexpected condition that prevented it from fulfilling the request.

Exception

jakarta.servlet.ServletException: Error instantiating servlet class [com.example.SampServlet]
    org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:542)
    org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
    org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:690)
    org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:356)
    org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:399)
    org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
    org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:867)
    org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1716)
    org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191)
    org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659)
    org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    java.base/java.lang.Thread.run(Thread.java:833)
Root Cause

java.lang.NoClassDefFoundError: javax/servlet/http/HttpServlet
    java.base/java.lang.ClassLoader.defineClass1(Native Method)
    java.base/java.lang.ClassLoader.defineClass(ClassLoader.java:1013)
    java.base/java.security.SecureClassLoader.defineClass(SecureClassLoader.java:150)
    org.apache.catalina.loader.WebappClassLoaderBase.findClassInternal(WebappClassLoaderBase.java:2527)
    org.apache.catalina.loader.WebappClassLoaderBase.findClass(WebappClassLoaderBase.java:877)
    org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1413)
    org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1257)
    org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:542)
    org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
    org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:690)
    org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:356)
    org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:399)
    org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
    org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:867)
    org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1716)
    org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191)
    org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659)
    org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    java.base/java.lang.Thread.run(Thread.java:833)
Root Cause

java.lang.ClassNotFoundException: javax.servlet.http.HttpServlet
    org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1449)
    org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1257)
    java.base/java.lang.ClassLoader.defineClass1(Native Method)
    java.base/java.lang.ClassLoader.defineClass(ClassLoader.java:1013)
    java.base/java.security.SecureClassLoader.defineClass(SecureClassLoader.java:150)
    org.apache.catalina.loader.WebappClassLoaderBase.findClassInternal(WebappClassLoaderBase.java:2527)
    org.apache.catalina.loader.WebappClassLoaderBase.findClass(WebappClassLoaderBase.java:877)
    org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1413)
    org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1257)
    org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:542)
    org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
    org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:690)
    org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:356)
    org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:399)
    org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
    org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:867)
    org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1716)
    org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191)
    org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659)
    org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    java.base/java.lang.Thread.run(Thread.java:833)
Note The full stack trace of the root cause is available in the server logs.

Solution

Tomcat 10.0 and above use the new Jakarta EE packages for code. This means, for example, that javax.servlet.http.HttpServlet is now jakarta.servlet.http.HttpServlet. The change started in version 9 of the EE spec thanks to Oracle and their hostility towards the development community.

Your code should start instead with something like:

import jakarta.servlet.*;
import jakarta.servlet.http.*;
import jakarta.servlet.annotation.*;
import java.io.IOException;
import java.io.PrintWriter;

@WebServlet(name = "SampServlet", value = "/SampServlet")
public class SampServlet extends HttpServlet {

to use the new specs. Tomcat also has an open source tool that can convert a larger code base from the EE 8 to EE 9 spec.

Answered By - stdunbar
Answer Checked By - Pedro (JavaFixing Volunteer)